Mafia is set in the Chicago of the 1920's and casts you as a small time criminal who has to become "boss of the underworld". Starting out with smaller crimes like robberies and smuggling alcohol, you gain points and eventually higher ranks. Gaining higher ranks means more respect from other criminals and potential victims, which in turn means that more lucrative crimes become available. Shopkeepers are more easily intimidated and therefore more easily robbed or blackmailed. You are also more likely to receive hints about upcoming crimes. After a certain rank has been reached, it is also possible to recruit up to ten gang members which gives you a much better chance in combat against the police or other criminals.
At the beginning of the game, your character is created by randomly determining various statistics:
Energy: the character's health, Strength: determines how fast energy is recovered, Intelligence: influences the odds of success of various crimes, Brutality: determines what kind of weapon a character can use.
The game is turn-based. One turn takes one month and at every turn you can take a certain amount of steps, depending on your method of transportation. Most of the game is spent walking around the town entering buildings where actions can be chosen from various multiple choice menus:
Try to blackmail or rob the store. The lower your rank, the higher the chance that the owner calls the police. If you try to blackmail someone who is already "protected" by another gangster, his gang might attack you.
Buy or sell alcohol, recruit gang members, get hints about upcoming crimes, get a job as a croupier, bouncer or assassin.
Buy weapons, train gang members (increase intelligence or brutality)
Buy or steal a car. Trying to steal a car is risky, but may be rewarded with especially fast cars that cannot be bought.
Rob a bank (this requires another gang-member), sneak into the bank and break into the safe (breaking into a safe starts a mini-game).
Buy false money (Blüten) or get a fake ID, which decreases the chances of getting busted during police checks.
Pickpocket people at the station or inside the subway car.
Pickpocket people or try to rob the train.
Play Black Jack, Poker or Roulette. You cannot actually play these games, you simply receive the results, which are influenced by your intelligence.
Lend money or start your own loan shark business.
Turn yourself in, bust out another criminal for a reward (only in multiplayer mode) or bribe the chief of police to avoid prosecution.
When fighting the police, other gangs or trying to assassinate somebody, the game enters combat mode. Combat is turn-based and seen from a top-down perspective. During each turn you can either move your character(s) by one field or attack. Winning a fight increases your points, however, losing a fight doesn't mean the game is over. Losing against other criminals simply means that you won't gain any money. After losing to the police you can still try to escape or bribe the police. When you do go to jail, you lose precious time and points.
Mafia can be played by up to four players. When it is played by more than one player, a "gang war" option becomes available.